The invention relates to the bracing of string sections, in particular pipe sections, to form a string, including a traction element which extends between an abutment on a forward end of the pipe string and an adapter on the rearward end thereof, a linear tensioning drive for applying a tension force, and a device for moving the tensioning drive out of a section.
Corresponding systems are oftentimes used for the trenchless pipe installation or renewal, for example to brace the pipe string comprised of individual pipe sections and to connect it with a leading drilling or bursting tool as clearance-free as possible.
Such a system is known, for example, from DE 196 08 056 C1 or U.S. Pat. No. 5,895,176.
A bursting tool is disclosed there which is pulled through an old pipe to be replaced. As the bursting tool advances through the old pipe, the old pipe is destroyed while at the same time a new pipe string is drawn into the ground. The newly-inserted pipe string is comprised of single short pipe sections.
In order to reduce friction during insertion, the pipe sections of the new pipe string have smooth sleeve joints on the outside and inside. These sleeve joints are, however, incapable to transmit tensile forces, requiring the provision of a tensioning device to realize a substantially play-free connection of the pipe string with the bursting tool.
The tensioning device acts upon a cable or a chain which is secured to the bursting tool and guided through the new pipe to be drawn in.
Disposed in the rearward end of the pipe string is the actual tensioning device which is supported on the rearward end of the last pipe section via an adapter.
The cable or chain is tightened by hydraulic cylinders which are arranged perpendicular to the cable or chain because of the tight space conditions that are frequently experienced in the working shafts. The cable or chain is hereby deflected in length direction of the hydraulic cylinder by a defection roller which is provided with a freewheel. The freewheel of the deflection roller prevents springback of the taut cable or taut chain when several cylinder strokes are necessary to attain a complete tensioning operation.
The tensioning device described in DE 196 08 056 C1 has many drawbacks.
As the deflection is required as a result of the vertical disposition of the cylinders, the use of flexible chains or cables is necessary as traction members which, when exposed to high tension forces, undergo, however, a significant length extension which must be compensated by the tensioning device. This is disadvantageous because the tensioning device must be detached each time a new pipe section is threaded on so that the elongated traction member is relieved and strained again during each tensioning cycle.
A further drawback of the afore-described tensioning device is the need for large space which it needs to occupy especially within a reversing shaft which oftentimes represents the starting point for replacing old pipes.
A further drawback of tensioning devices, using a cable or a chain as traction member is normally the need for the cable or chain to have an overall length which is at least as long as the pipe string to be drawn in. The pipe sections must be threaded over a long path onto the traction member, in particular when the pipe renewal process begins.
DE 10 2004 033 566 B3 describes a device for bracing pipe section to form a pipe string, including a traction element, which extends between an abutment on the forward end of the pipe string and an adapter on the rearward end thereof, and a linear tensioning drive for applying a tension force. The system is characterized by the parallel disposition of the linear tensioning drive in relation to the pipe string, whereby one side of the linear tensioning drive is supported on the adapter and the other side is supported on the traction element via at least one holding element.
This enables the linear tensioning drive to be arranged in part also within the pipe string to be installed and reduces the space demand of the tensioning device.
On the other hand, the tensioning device must be moved on the traction element or detached from the traction element in order to add another pipe section to the pipe string. This is done heretofore by hand.